Method to purify aluminum and use of purified aluminum to purify silicon

ABSTRACT

The present invention provides a method of purifying aluminum, and/or use of the purified aluminum as a solvent metal to purify silicon.

RELATED APPLICATIONS

This application claims the benefit of priority to U.S. ProvisionalApplication No. 61/663,871, filed Jun. 25, 2012, which is herebyincorporated by reference in its entirety.

BACKGROUND

Solar cells are currently utilized as an energy source by using theirability to convert sunlight to electrical energy. Silicon is used almostexclusively as the semiconductor material in such photovoltaic cells. Asignificant limitation currently on the use of solar cells has to dowith the cost of purifying silicon to solar grade (SG). In view ofcurrent energy demands and supply limitations, there is an enormous needfor a more cost efficient way of purifying metallurgical grade (MG)silicon (or any other silicon having greater impurities than solargrade) to solar grade silicon.

Companies and research groups have been working on making upgradedmetallurgical (UMG) silicon. Many of these processes are limited in thatthey have difficulty reducing the amount of boron. For example, theprocess of purifying silicon via an aluminum solvent is ultimatelylimited by the purity of the aluminum used. The amount of naturallyoccurring boron in aluminum is relatively low and can be screened fromthe population of castings at the primary producer's site. This cangenerally provide aluminum with boron content in the range of 0.6 ppmw.While this is sufficient to produce silicon crystals in the range of 0.4ppmw, this level of boron is still considered too high to produce solarcells which do not suffer from degraded breakdown voltages. It may bepossible to further improve the boron content downstream, but thisapproach presents its own challenges.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a block flow diagram of a method of purifyingaluminum.

FIG. 2 illustrates a block flow diagram of a method of purifyingsilicon.

FIG. 3 illustrates a block flow diagram of a method of purifyingaluminum.

SUMMARY

The present invention provides a method for purifying aluminum. Themethod includes: (a) forming a molten liquid from aluminum and a metaladditive selected from titanium, vanadium, zirconium, chromium, andcombinations thereof; (b) allowing impurities to form in the moltenliquid, wherein the impurities include a reaction product of the metaladditive and boron; (b) optionally removing at least a portion of theimpurities from the molten liquid; (d) cooling the molten liquid to formsolidified aluminum; and (e) optionally removing a portion of thesolidified aluminum including at least a portion of the impurities;wherein at least one of the optional steps is carried out, to providepurified aluminum.

The present invention also provides a method for purifying aluminum. Themethod includes: (a) forming a molten liquid from aluminum and titanium;(b) allowing impurities to form in the molten liquid, wherein theimpurities include a reaction product of the titanium and boron; (b)optionally removing at least a portion of the impurities from the moltenliquid; (d) cooling the molten liquid to form solidified aluminum; and(e) optionally removing a portion of the solidified aluminum includingat least a portion of the impurities; wherein at least one of theoptional steps is carried out, to provide purified aluminum.

The present invention also provides a method for purifying silicon. Themethod includes: (a) forming a molten liquid from silicon and aluminum,wherein the aluminum includes less than about 0.55 ppmw boron; (b)cooling the molten liquid, to form silicon crystals and a mother liquor;and (e) separating the silicon crystals and the mother liquor.

The process described herein employs reactive chemistry to achieve areduction in the boron level of aluminum. In doing so, the metaladditive (e.g., titanium) reacts with boron to form boron-containingimpurities (e.g., TiB₂ particles). If the molten aluminum bath istreated with metal additive (e.g., titanium), boron-containingimpurities (e.g., TiB₂ particles) can form, and can be physicallyseparated from the majority of the aluminum. For example, theboron-containing impurities (e.g., TiB₂ particles) can settle to thebottom of the bath, and can then be physically separated from themajority of the aluminum. This can effectively reduce the level of boronin the aluminum, e.g., to below about 0.2 ppmw. The effect of this boronreduction on a subsequent process to purify silicon can be immediatelyevident. It is believed that there will be no adverse affects on solarcells, and as such, this represents an additional advantage in utilizingthe metal additive (e.g., titanium) for the removal of boron. Theultimate boron level in the final silicon crystals can therefore belowered, without the introduction of an impurity having negativeattributes when present in the subsequent silicon purification processsteps.

The present invention provides a method of purifying aluminum, and/oruse of the purified aluminum as a solvent metal to purify silicon.Utilizing such methods, purified materials (e.g., aluminum and/orsilicon) can be obtained, having relatively low amounts of boron. Moreconsistent concentrations of impurities in the purified materials can beobtained. A purified material of more consistent quality can beobtained. The production of purified silicon crystals that can be usedto generate higher quality products can be obtained. The methods can becarried out in a relatively cost-effective manner, while utilizingmaterials that are relatively cost-effective. A substance (e.g, metaladditive, such as titanium) can be introduced during the process topurify aluminum, wherein that substance does not have any significant orappreciable adverse affects on solar cells. A substance (e.g,boron-containing substance, such as TiB₂) can be formed during theprocess to purify aluminum, wherein any remaining amount of thatsubstance not removed, does not have any significant or appreciableadverse affects on solar cells. Less pure starting aluminum can beemployed as a solvent metal in the purification of silicon. The abilityto use less pure starting aluminum can lower cost and access to agreater supply of raw material. The production of purified siliconcrystals can therefore be accomplished, in a relatively cost-effectivemanner.

DETAILED DESCRIPTION

The following detailed description includes references to theaccompanying drawings, which form a part of the detailed description.The drawings show, by way of illustration, specific embodiments in whichthe invention may be practiced. These embodiments, which are alsoreferred to herein as “examples,” are described in enough detail toenable those skilled in the art to practice the invention. Theembodiments may be combined, other embodiments may be utilized, orstructural, and logical changes may be made without departing from thescope of the present invention. The following detailed description is,therefore, not to be taken in a limiting sense, and the scope of thepresent invention is defined by the appended claims and theirequivalents.

In this document, the terms “a” or “an” are used to include one or morethan one and the term “or” is used to refer to a nonexclusive “or”unless otherwise indicated. In addition, it is to be understood that thephraseology or terminology employed herein, and not otherwise defined,is for the purpose of description only and not of limitation.Furthermore, all publications, patents, and patent documents referred toin this document are incorporated by reference herein in their entirety,as though individually incorporated by reference. In the event ofinconsistent usages between this document and those documents soincorporated by reference, the usage in the incorporated referenceshould be considered supplementary to that of this document; forirreconcilable inconsistencies, the usage in this document controls.

In the methods of manufacturing described herein, the steps can becarried out in any order without departing from the principles of theinvention, except when a temporal or operational sequence is explicitlyrecited. Recitation in a claim to the effect that first a step isperformed, then several other steps are subsequently performed, shall betaken to mean that the first step is performed before any of the othersteps, but the other steps can be performed in any suitable sequence,unless a sequence is further recited within the other steps. Forexample, claim elements that recite “Step A, Step B, Step C, Step D, andStep E” shall be construed to mean step A is carried out first, step Eis carried out last, and steps B, C, and D can be carried out in anysequence between steps A and E, and that the sequence still falls withinthe literal scope of the claimed process. A given step or sub-set ofsteps may also be repeated.

Furthermore, specified steps can be carried out concurrently unlessexplicit claim language recites that they be carried out separately. Forexample, a claimed step of doing X and a claimed step of doing Y can beconducted simultaneously within a single operation, and the resultingprocess will fall within the literal scope of the claimed process.

Definitions

As used herein, “purifying” refers to the physical separation of asubstance of interest from one or more foreign or contaminatingsubstances. In contrast, “impurities” or “impurity” refers to the one ormore foreign or contaminating substances that are undesirable.

As used herein, “molten” or “molten liquid” refers to one or moresubstances, together, that are melted.

As used herein, “melting” refers to the process of heating one or moresolid substances to a point (called the melting point), or above, wherethey turn into a liquid. As such, the “melting” refers to a substancechanging from a solid to a liquid, when exposed to sufficient heat.

As used herein, “aluminum” refers to the chemical element that has thesymbol Al and atomic number 13. The term includes metal aluminum orelemental aluminum (Al⁰), or an alloy thereof. The aluminum willtypically be used as a solvent metal.

As used herein, “solvent metal” refers to one or more metals, or analloy thereof, which upon heating, can effectively dissolve silicon,resulting in a molten liquid. Suitable exemplary solvent metals include,e.g., aluminum or an alloy thereof, and optionally at least one ofcopper, tin, zinc, antimony, silver, bismuth, cadmium, gallium, indium,magnesium, lead, and alloys thereof.

As used herein, an “alloy” refers to a homogeneous mixture of two ormore elements, at least one of which is a metal, and where the resultingmaterial has metallic properties. The resulting metallic substanceusually has different properties (sometimes significantly different)from those of its components.

As used herein, “titanium” refers to the chemical element that has thesymbol Ti and atomic number 22. The term includes metal titanium orelemental titanium)(Ti⁰), as well as an alloy thereof The titanium willtypically be used to remove boron from the solvent metal (e.g.,aluminum), by complexing with boron-containing impurities.

As used herein, “vanadium” refers to the chemical element that has thesymbol V and atomic number 23. The term includes metal vanadium orelemental vanadium) (V⁰), as well as an alloy thereof. The vanadium willtypically be used to remove boron from the solvent metal (e.g.,aluminum), by complexing or reacting with boron-containing impurities.

As used herein, “zirconium” refers to the chemical element refers to thechemical element that has the symbol Zr and atomic number 40. The termincludes metal zirconium or elemental zirconium) (Zr⁰), as well as analloy thereof. The zirconium will typically be used to remove boron fromthe solvent metal (e.g., aluminum), by complexing or reacting withboron-containing impurities.

As used herein, “chromium” refers to the chemical element refers to thechemical element that has the symbol Cr and atomic number 24. The termincludes metal chromium or elemental chromium) (Cr⁰), as well as analloy thereof. The chromium will typically be used to remove boron fromthe solvent metal (e.g., aluminum), by complexing or reacting withboron-containing impurities.

As used herein, a “reaction product” refers to a compound formed by thechemical reaction of two or more substances. An exemplary reactionproduct of titanium and boron includes titanium diboride (TiB₂).

As used herein, “coordination complex,” “metal complex” or “complex”refers to an atom or ion (usually metallic, such as titanium, vanadium,zirconium or chromium), bonded to a surrounding array of molecules oranions (including, e.g., boron), that are in turn known as ligands orcomplexing agents. Many metal-containing compounds consist ofcoordination complexes.

As used herein, “solidifying” refers to the process of cooling one ormore liquid substances (e.g., molten liquid) below a point (called themelting point), where they turn into a solid. As such, the “solidifying”refers to a substance changing from a liquid to a solid, upon cooling.

As used herein, “removing” refers to the process of separating asubstance from another substance (e.g., removing a solid or a liquidfrom a mixture) or separating a portion of a substance from anotherportion (e.g., removing a part of a solid from another part of thesolid). The process can employ any technique known to those of skill inthe art, e.g., decanting the mixture, skimming one or more liquids fromthe mixture, centrifuging the mixture, filtering the solids from themixture, cutting a solid to remove a portion thereof, or a combinationthereof.

As used herein, “boron” refers to the chemical element that has thesymbol B and atomic number 5. The term includes compounds that includeboron (i.e., boron-containing compounds that include B³⁺, B²⁺, or B⁺),and combinations thereof.

As used herein, “silicon” refers to the chemical element that has thesymbol Si and atomic number 14. The term includes metal or elementalsilicon (Si⁰), or an alloy thereof.

As used herein, “metallurgical grade silicon” refers to relatively pure(e.g., at least about 96.0 wt. %) silicon.

As used herein, “crystalline” includes the regular, geometricarrangement of atoms in a solid. As such, “silicon crystals” refers tosilicon having regular, geometric arrangement of the silicon atoms in asolid state.

As used herein, “contacting” refers to the act of touching, makingcontact, or of bringing substances into immediate proximity.

As used herein, “decanting” or “decantation” includes pouring off afluid, leaving a sediment or precipitate, thereby separating the fluidfrom the sediment or precipitate.

As used herein, “filtering” or “filtration” refers to a mechanicalmethod to separate solids from liquids by passing the feed streamthrough a porous sheet such as a ceramic or metal membrane, whichretains the solids and allows the liquid to pass through. This can beaccomplished by gravity, pressure or vacuum (suction). The filteringeffectively separates the sediment and/or precipitate from the liquid.

Referring to FIG. 1, an example of a block flow diagram 100 of a methodfor purifying aluminum is shown, according to some embodiments. A moltenliquid 106 is formed from heating 104 aluminum 101 and metal additive102. Impurities can optionally be removed 108 from the molten liquid 106to provide a purified molten 110. Either the molten liquid 106 or thepurified molten 110 is cooled 112, to provide the solidified aluminum114. A portion of the solidified aluminum 114 can optionally be removed116 to provide purified solid aluminum 118.

A molten liquid 106 is formed from heating 104 aluminum 101 and metaladditive 102. The heating of the aluminum 101 and metal additive 102 iscarried out, to achieve a temperature that will effectively form amolten liquid 106. For example, the temperature can be at least about650° C.

Any suitable amount of metal additive 102 can be employed, provided theamount of metal additive 102 effectively provides impurities from themolten liquid 106 that can be effectively removed. For example, at leastabout 200 ppmw metal additive 102 can be employed, relative to thealuminum 101.

The metal additive 102 will typically be used to remove impurities(e.g., boron-containing impurities) from the solvent metal (e.g.,aluminum 101). As such, aluminum 101 can be purified from boron, suchthat at least some of the boron is removed from the aluminum 101. Forexample, the aluminum 101 can include at least about 0.30 ppmw boron.

The boron-containing impurities will typically include a reactionproduct of metal additive 102 and boron, such as, e.g., titaniumdiboride (TiB₂). Additional impurities include those impurities formedfrom the reaction product of metal additive, boron, and an additionalsubstance present in the molten liquid or which contacts the moltenliquid. Additional impurities include those impurities formed from thereaction product of boron and an additional substance present in themolten liquid or which contacts the molten liquid, wherein generation ofthe reaction product is catalyzed by, or coordinated with, the metaladditive 102. An exemplary substance present in the molten liquid, orwhich contacts the molten liquid, includes, e.g., oxygen.

The aluminum 101 and metal additive 102 can be present together, in thealuminum 101. In such an embodiment, the aluminum 101 will include asignificant and appreciable amount of metal additive 102. Alternatively,the aluminum 101 and metal additive 102 can be separately added, eitherconcurrently or consecutively. In such an embodiment, the molten liquid106 can be formed from aluminum 101, and the metal additive 102 cansubsequently be added. Alternatively, the molten liquid 106 can beformed from metal additive 102, and the aluminum 101 can subsequently beadded. Alternatively, the molten liquid 106 can be formed from aluminum101 and metal additive 102, and together they can be heated. In anysuitable manner as described above, the molten liquid 106 is formed fromheating 104 aluminum 101 and metal additive 102.

The impurities are allowed to form in the molten liquid 106, where theycan optionally be removed 108. In specific embodiments, the impuritieswill move toward the bottom of the vessel containing the molten liquid106. In such embodiments, the impurities can optionally be removed 108,e.g., by decanting or filtering.

The impurities are allowed to form in the molten liquid 106. It isappreciated that those of skill in the art of metallurgical chemistryunderstand that in the process of forming impurities in the moltenliquid 106, matter is not being created. Instead, at least a portion ofthe boron-containing impurities present in the molten liquid 106 (fromthe aluminum 101) will complex in the molten liquid 106. Theseboron-containing impurities will be transformed to new boron-containingimpurities (e.g., a reaction product of metal additive and boron) thatcan optionally be removed from the molten liquid 106.

In specific embodiments, the optional step of removing the at least aportion of the impurities 108 from the molten liquid 106 is carried out.In alternative specific embodiments, the optional step of removing theat least a portion of the impurities 108 from the molten liquid 106 isnot carried out.

The molten liquid 106 can be cooled 112 to form a solidified aluminum114. Alternatively, the purified molten 110 can be cooled 112 to form asolidified aluminum 114. The cooling 112 can be carried out in anysuitable manner, provided the solidified aluminum 114 is obtained. Forexample, the cooling 112 can be carried out at about room temperature(about 20° C.), for an extended period of time.

Upon cooling 112, a portion of the solidified aluminum 114 canoptionally be removed 116. In those specific embodiments in which theimpurities will move toward the bottom of the vessel containing themolten liquid 106, the bottom portion of the solidified aluminum 114 canbe removed (i.e., the portion of the solidified aluminum 114 including asignificant amount of the impurities). That portion of the solidifiedaluminum 114 can be removed by any suitable means. For example, thatportion of the solidified aluminum 114 can be mechanically removed, forexample, by cutting the solidified aluminum 114.

Alternatively, in those specific embodiments in which the impuritieswill move toward the sides of the vessel containing the molten liquid106, the side portions of the solidified aluminum 114 can be removed(i.e., the portion of the solidified aluminum 114 including asignificant amount of the impurities). Moving the impurities toward thesides of the vessel containing the molten liquid 106 can beaccomplished, e.g., by spinning or centrifuging the vessel containingthe molten liquid 106.

Alternatively, in those specific embodiments in which the impuritieswill move toward the top of the vessel containing the molten liquid 106,the top portions of the solidified aluminum 114 can be removed (i.e.,the portion of the solidified aluminum 114 including a significantamount of the impurities). Moving the impurities toward the top of thevessel containing the molten liquid 106 can be accomplished, e.g., byintroducing substances to the molten liquid 106 that will result in theimpurities floating or rising to the surface of the molten liquid 106.

In specific embodiments, the optional step of removing a portion of thesolidified aluminum 116 is carried out. In alternative specificembodiments, the optional step of removing a portion of the solidifiedaluminum 116 is not carried out.

In specific embodiments, the optional step of removing the at least aportion of the impurities from the molten liquid 108 is carried out, andthe optional step of removing a portion of the solidified aluminum is116 carried out.

In specific embodiments, the method for purifying aluminum 100 can becarried out once. In alternative specific embodiments, the method forpurifying aluminum 100 can be carried out two or more (e.g., 2, 3 or 4)times.

The method for purifying aluminum 100 provides purified solid aluminum118 that is relatively pure, compared to the starting aluminum 101. Thispurified solid aluminum 118 can then be used, e.g., as a solvent metalfor the purification of silicon (see, FIG. 2). For example, the methodfor purifying aluminum 100 provides purified solid aluminum 118 that ispurified from boron, such that at least some of the boron is removedfrom the starting aluminum 101. As such, a significant and appreciableamount of boron present in the starting aluminum 101 can be removed toprovide the purified solid aluminum 118.

Referring to FIG. 3, an example of a block flow diagram 300 of a methodfor purifying aluminum is shown, according to some embodiments. A moltenliquid 306 is formed from heating 304 aluminum 301 and titanium 302.Impurities can optionally be removed 308 from the molten liquid 306 toprovide a purified molten 310. Either the molten liquid 306 or thepurified molten 310 is cooled 312, to provide the solidified aluminum314. A portion of the solidified aluminum 314 can optionally be removed316 to provide purified solid aluminum 318.

A molten liquid 306 is formed from heating 304 aluminum 301 and titanium302. The heating of the aluminum 301 and titanium 302 is carried out, toachieve a temperature that will effectively form a molten liquid 306.For example, the temperature can be at least about 650° C.

Any suitable amount of titanium 302 can be employed, provided the amountof titanium 302 effectively provides impurities from the molten liquid306 that can be effectively removed. For example, at least about 200ppmw titanium 302 can be employed, relative to the aluminum 301.

The titanium 302 will typically be used to remove impurities (e.g.,boron-containing impurities) from the solvent metal (e.g., aluminum301). As such, aluminum 301 can be purified from boron, such that atleast some of the boron is removed from the aluminum 301. For example,the aluminum 301 can include at least about 0.30 ppmw boron.

The boron-containing impurities will typically include a reactionproduct of titanium 302 and boron, such as, e.g., titanium diboride(TiB₂). Additional impurities include those impurities formed from thereaction product of titanium, boron, and an additional substance presentin the molten liquid or which contacts the molten liquid. Additionalimpurities include those impurities formed from the reaction product ofboron and an additional substance present in the molten liquid or whichcontacts the molten liquid, wherein generation of the reaction productis catalyzed by, or coordinated with, the titanium 302. An exemplarysubstance present in the molten liquid, or which contacts the moltenliquid, includes, e.g., oxygen.

The aluminum 301 and titanium 302 can be present together, in thealuminum 301. In such an embodiment, the aluminum 301 will include asignificant and appreciable amount of titanium 302. Alternatively, thealuminum 301 and titanium 302 can be separately added, eitherconcurrently or consecutively. In such an embodiment, the molten liquid306 can be formed from aluminum 301, and the titanium 302 cansubsequently be added. Alternatively, the molten liquid 306 can beformed from titanium 302, and the aluminum 301 can subsequently beadded. Alternatively, the molten liquid 306 can be formed from aluminum301 and titanium 302, and together they can be heated. In any suitablemanner as described above, the molten liquid 306 is formed from heating304 aluminum 301 and titanium 302.

The impurities are allowed to form in the molten liquid 306, where theycan optionally be removed 308. In specific embodiments, the impuritieswill move toward the bottom of the vessel containing the molten liquid306. In such embodiments, the impurities can optionally be removed 308,e.g., by decanting or filtering.

The impurities are allowed to form in the molten liquid 306. It isappreciated that those of skill in the art of metallurgical chemistryunderstand that in the process of forming impurities in the moltenliquid 306, matter is not being created. Instead, at least a portion ofthe boron-containing impurities present in the molten liquid 306 (fromthe aluminum 301) will complex in the molten liquid 306. Theseboron-containing impurities will be transformed to new boron-containingimpurities (e.g., a reaction product of titanium and boron) that canoptionally be removed from the molten liquid 306.

In specific embodiments, the optional step of removing the at least aportion of the impurities 308 from the molten liquid 306 is carried out.In alternative specific embodiments, the optional step of removing theat least a portion of the impurities 308 from the molten liquid 306 isnot carried out.

The molten liquid 306 can be cooled 312 to form a solidified aluminum314. Alternatively, the purified molten 310 can be cooled 312 to form asolidified aluminum 314. The cooling 312 can be carried out in anysuitable manner, provided the solidified aluminum 314 is obtained. Forexample, the cooling 312 can be carried out at about room temperature(about 20° C.), for an extended period of time.

Upon cooling 312, a portion of the solidified aluminum 314 canoptionally be removed 316. In those specific embodiments in which theimpurities will move toward the bottom of the vessel containing themolten liquid 306, the bottom portion of the solidified aluminum 314 canbe removed (i.e., the portion of the solidified aluminum 314 including asignificant amount of the impurities). That portion of the solidifiedaluminum 314 can be removed by any suitable means. For example, thatportion of the solidified aluminum 314 can be mechanically removed, forexample, by cutting the solidified aluminum 314.

Alternatively, in those specific embodiments in which the impuritieswill move toward the sides of the vessel containing the molten liquid306, the side portions of the solidified aluminum 314 can be removed(i.e., the portion of the solidified aluminum 314 including asignificant amount of the impurities). Moving the impurities toward thesides of the vessel containing the molten liquid 306 can beaccomplished, e.g., by spinning or centrifuging the vessel containingthe molten liquid 306.

Alternatively, in those specific embodiments in which the impuritieswill move toward the top of the vessel containing the molten liquid 306,the top portions of the solidified aluminum 314 can be removed (i.e.,the portion of the solidified aluminum 314 including a significantamount of the impurities). Moving the impurities toward the top of thevessel containing the molten liquid 306 can be accomplished, e.g., byintroducing substances to the molten liquid 306 that will result in theimpurities floating or rising to the surface of the molten liquid 306.

In specific embodiments, the optional step of removing a portion of thesolidified aluminum 316 is carried out. In alternative specificembodiments, the optional step of removing a portion of the solidifiedaluminum 316 is not carried out.

In specific embodiments, the optional step of removing the at least aportion of the impurities from the molten liquid 308 is carried out, andthe optional step of removing a portion of the solidified aluminum is316 carried out.

In specific embodiments, the method for purifying aluminum 300 can becarried out once. In alternative specific embodiments, the method forpurifying aluminum 300 can be carried out two or more (e.g., 2, 3 or 4)times.

The method for purifying aluminum 300 provides purified solid aluminum318 that is relatively pure, compared to the starting aluminum 301. Thispurified solid aluminum 318 can then be used, e.g., as a solvent metalfor the purification of silicon (see, FIG. 2). For example, the methodfor purifying aluminum 300 provides purified solid aluminum 318 that ispurified from boron, such that at least some of the boron is removedfrom the starting aluminum 301. As such, a significant and appreciableamount of boron present in the starting aluminum 301 can be removed toprovide the purified solid aluminum 318.

Referring to FIG. 2, an example of a block flow diagram 200 of a methodfor purifying silicon is shown, according to some embodiments. A moltenliquid 206 is formed from silicon 201 and aluminum 202. The moltenliquid 206 is cooled 208 to provide silicon crystals and mother liquor210. The silicon crystals and mother liquor 210 are separated, toprovide silicon crystals 214 and mother liquor 216.

A molten liquid 206 is formed from silicon 201 and aluminum 202. Theheating 204 of the aluminum 202 and silicon 201 is carried out, toachieve a temperature that will effectively form a molten liquid 206.For example, heating 204 of the aluminum 202 and silicon 201 can becarried out, to achieve a temperature of at least about 1420° C.

Silicon 201 for processing may be generated from a number of sources.The silicon 201 may be scrap or discarded silicon from manufacturingsolar cell panels, semiconductor wafers or shaping ingots, for example.Often the silicon 201 is part of a slurry. The slurry may include water,polyethylene glycol (PEG), silicon carbide, iron, aluminum, calcium,copper and other contaminants. The silicon 201 may be removed from theslurry (e.g., separated) and dried to remove excess water. The powdermay be separated from the slurry by centrifuge, settling or otherprocesses. Adding water to the slurry can lower the specific gravity tohelp improve the settling or centrifuging. The silicon 201 may undergofurther processing to remove contaminants, such as by undergoing an acidtreatment, for example. For example, hydrochloric acid can be used todissolve the metals, such as iron, off of the surface of the siliconpowder. Hydrofluoric acid, hydrochloric acid, nitric acid or acombination thereof may be used to dissolve silicon dioxide off of thesurface of the powder or to dissolve the surface of the powder.Alternatively, potassium hydroxide, sodium hydroxide or a combinationthereof may be used to dissolve the surface of the powder. The powdermay also be treated with a magnetic separating process to remove ironand other magnetic elements.

Alternatively, in specific embodiments, the silicon 201 employed can bethe silicon crystals 214 obtained in a previous purification process.Specifically, the method for purifying silicon 200 can provide siliconcrystals 214. These silicon crystals 214 can then be employed (assilicon 201) in a subsequent method for purifying silicon 200. This canbe carried out one or more (e.g., two, three of four) times.

Specifically, the silicon 201 can include metallurgical grade (MG)silicon. Alternatively, the silicon 201 can be of a grade or qualitythat is below metallurgical grade (MG) silicon. Employing less puresilicon (e.g., silicon of a grade or quality that is below metallurgicalgrade (MG) silicon) can provide cost-savings, as well as allowing forthe use of silicon that would otherwise not be feasible or practical.

The molten liquid 206 can be formed from silicon 201 and aluminum 202.The silicon 201 can be heated 204 under submersion, thus limiting orpreventing the silicon 201 from contacting an oxygenated environment. Bylimiting such contact with oxygen, the silicon 201 has less chance toreact to form the undesirable product silicon dioxide. By submerging thesilicon 201 during melting, expensive and complicated steps areunnecessary, such as having to use a vacuum or inert gas atmosphere, forexample. Additionally, prior to contacting silicon 201 with aluminum,the silicon 201 can be pretreated with an acid treatment, magneticseparation, vacuum melting, drying or a combination thereof. One or moreof these steps may facilitate the removal of contaminants, such as iron.

The molten liquid 206 can be formed from silicon 201 and aluminum 202,such as by feeding into a vortex using a rotary degasser, molten metalpump, rotary furnace or by induction currents. The silicon 201 may besubstantially dried and fed consistently into the vortex, thus limitingits contact with oxygen. The silicon 201 may be sheared into individualgrains, such as by setting the mixer settings for high shear. Themelting may occur under submersion in a molten bath. For example, thebath may be below the liquidus temperature and above the solidustemperature, so that it is easier to put more shear on the powder andeasier to keep the powder submerged in the bath due to the increasedviscosity of the bath. The furnace refractory may be low incontaminates, such as by having little to no phosphorus or boron in thematerial. Fused silica and/or fused alumina may be an example of anacceptable refractory. Similarly, if a rotary degasser or molten metalpump is utilized, they may be manufactured with little phosphorus orboron to minimize contamination.

The silicon 201 and aluminum 202 may be kept submerged by utilizing meltturbulence. The melting may occur under mixing conditions in which thetemperature is maintained above the solidus temperature. The meltingprovides a molten liquid 206.

The silicon 201 and solvent metal (e.g., aluminum 202) can each bepresent in any suitable amount or ratio, provided the molten liquid 206can effectively be formed (after heating 204). For example, the silicon201 can be employed in about 20 wt. % to about 50 wt. %, and aluminum202 can be employed as the solvent metal, in about 50 wt. % to about 80wt. %. Utilizing silicon waste streams, the silicon 201 may be presentin about 20 wt. % to about 90 wt. % or more. Aluminum 202 may be thenemployed as the solvent metal in a ratio of less than about 10 wt. % toabout 80 wt. % for example. The silicon 201 may be used as the onlysource of silicon, or may be used as a percentage of the silicon addedto the process. By varying the amounts and types of silicon used in theprocess, the chemistry of the resultant purified silicon may be changedor controlled.

The aluminum 202 will typically be used as a solvent metal, to removeimpurities from the silicon 201. Utilizing aluminum 202 that isrelatively pure (while being relatively inexpensive) is typicallyadvantageous, especially in the solar industry. As such, the aluminum202 employed in the method to purify silicon can be the purified solidaluminum 118, as described herein (see, FIG. 1 or FIG. 3). For example,the aluminum 202 can include up to about 0.75 ppmw boron.

The aluminum 202 and silicon 201 can be present together. Specifically,the molten liquid 206 can be formed from aluminum 202 and silicon 201,wherein together they can be heated to form the molten liquid 206.Additionally, the aluminum 202 and silicon 201 can be separately added,either concurrently or consecutively. Alternatively, the molten liquid206 can be formed from aluminum 202, and the silicon 201 cansubsequently be added. Alternatively, the molten liquid 206 can beformed from silicon 201, and the aluminum 202 can subsequently be added.In any suitable manner as described above, the molten liquid 206 isformed from heating 204 aluminum 202 and silicon 201.

The molten liquid 206 can be cooled 208 to form silicon crystals andmother liquor 210. The cooling 208 can be carried out in any suitablemanner, provided the silicon crystals and mother liquor 210 areobtained. For example, the cooling 208 can be carried out at a suitabletemperature, e.g., at about room temperature (20° C.), for an extendedperiod of time. Additionally, the cooling 208 can be carried out at asuitable rate, e.g., up to about 150° C./hr.

Upon cooling 208, the silicon crystals and mother liquor 210 can beseparated, to provide separated silicon crystals 214 and mother liquor216. The separation can be carried out utilizing any suitable technique,such as, e.g., decanting (e.g., pouring off the mother liquor from thesilicon crystals), and/or filtering.

As stated above, the molten liquid 206 may be cooled 208 to providesilicon crystals 214 and a mother liquor 216. In one embodiment, themolten liquid 206 can be cooled 208 without any significant orappreciable agitation of the molten liquid 206. Alternatively, themolten liquid 206 can be cooled 208 while agitating the molten liquid206. Without being bound to any particular theory, it is believed thatduring the cooling 208, agitating can provide relatively small siliconcrystals, which can be difficult to strain, of a relatively high purity.In specific embodiments, a small amount of mixing can provide siliconcrystals of about 1 mm (thickness), by about 5 mm (width), by about 5 mm(length).

Additionally, the molten liquid 206 can be cooled 208 to any suitableand appropriate temperature (such as between the liquidus and solidustemperature), provided silicon crystals are obtained in a mother liquor216. For example, the molten liquid 206 can be cooled 208 to atemperature of about 585-1400° C.

The molten liquid 206 can be cooled 208 at any suitable any appropriaterate, provided silicon crystals 214 are obtained in a mother liquor 216.For example, the molten liquid 206 can be cooled 208 at a rate of up toabout 150° C./hr.

The molten liquid 206 can be cooled 208 over any suitable andappropriate period of time, provided silicon crystals are obtained in amother liquor 216. For example, the molten liquid 206 can be cooled 208over a period of time of at least about 2 hours.

The silicon crystals 214 and the mother liquor 216 can be separated 212.The separation 212 can be carried out in any suitable and appropriatemanner. For example, the separation 212 can be carried out by pouringoff the mother liquor 216 from the silicon crystals 214. Alternatively,the separation 212 can be carried out by straining and/or filtering thesilicon crystals 214 from the mother liquor 216. Alternatively, theseparation 212 can be carried out employing centrifugation.

In one specific embodiment, the silicon crystals 214 obtained can beemployed or re-used as the silicon 201 in a subsequent purification.This re-use can be carried out multiple times (e.g., 2, 3, 4 or 5), toprovide silicon crystals 214 having a requisite purity level. As such,the method for purifying silicon 200, to provide silicon crystals 214,can be carried out once. In alternative embodiments, the method forpurifying silicon 200, to provide silicon crystals 214, can be carriedout two or more (e.g., 2, 3, 4 or 5) times.

The method for purifying silicon 200 provides silicon crystals 214 thatare relatively pure, compared to the silicon 201. These silicon crystals214 can then be used, with or without subsequent purification, e.g., inthe manufacturing of solar cells, which can subsequently be used in themanufacturing of solar panels. The method for purifying silicon 200provides silicon crystals 214 that are purified from boron, such that atleast some of the boron is removed from the starting silicon 201. Forexample, the silicon crystals 214 can include less than about 0.55 ppmwboron. Additionally, up to about 85 wt. % of boron present in thestarting silicon 201 can be removed to provide the silicon crystals 214.The resulting silicon crystals 214 will therefore be relatively pure.For example, the silicon crystals 214 can include silicon in at leastabout 65 wt. %.

Specific ranges, values, and embodiments provided below are forillustration purposes only and do not otherwise limit the scope of thedisclosed subject matter, as defined by the claims. The specific ranges,values, and embodiments described below encompass all combinations andsub-combinations of each disclosed range, value, and embodiment, whetheror not expressly described as such.

Specific Ranges, Values, and Embodiments

The metal additive 102 can include titanium, vanadium, zirconium,chromium, or a combination thereof. In specific embodiments, the metaladditive 102 can include vanadium, zirconium, chromium, or a combinationthereof. In additional specific embodiments, the metal additive 102 caninclude titanium, zirconium, chromium, or a combination thereof. Inadditional specific embodiments, the metal additive 102 can includetitanium, vanadium, chromium, or a combination thereof. In additionalspecific embodiments, the metal additive 102 can include titanium,vanadium, zirconium, or a combination thereof. In additional specificembodiments, the metal additive 102 can include titanium, vanadium, or acombination thereof. In additional specific embodiments, the metaladditive 102 can include titanium, zirconium, or a combination thereof.In additional specific embodiments, the metal additive 102 can includetitanium, chromium, or a combination thereof. In additional specificembodiments, the metal additive 102 can include vanadium, zirconium, ora combination thereof. In additional specific embodiments, the metaladditive 102 can include vanadium, chromium, or a combination thereof.In additional specific embodiments, the metal additive 102 can includezirconium, chromium, or a combination thereof. In additional specificembodiments, the metal additive 102 can include titanium. In additionalspecific embodiments, the metal additive 102 can include vanadium. Inadditional specific embodiments, the metal additive 102 can includezirconium. In additional specific embodiments, the metal additive 102can include chromium.

In specific embodiments, the heating of the aluminum 101 and metaladditive 102 can be carried out, to achieve a temperature of at leastabout 750° C. In additional specific embodiments, the heating of thealuminum 101 and metal additive 102 can be carried out, to achieve atemperature of at least about 950° C. In additional specificembodiments, the heating of the aluminum 101 and metal additive 102 canbe carried out, to achieve a temperature of about 650° C. to about 1750°C. In additional specific embodiments, the heating of the aluminum 101and metal additive 102 can be carried out, to achieve a temperature ofabout 700° C. to about 1670° C.

In specific embodiments, at least about 500 ppmw metal additive 102 canbe employed, relative to the aluminum 101. In additional specificembodiments, at least about 1,000 ppmw metal additive 102 can beemployed, relative to the aluminum 101. In additional specificembodiments, at least about 1,500 ppmw metal additive 102 can beemployed, relative to the aluminum 101. In additional specificembodiments, at least about 2,000 ppmw metal additive 102 can beemployed, relative to the aluminum 101. In additional specificembodiments, at least about 2,500 ppmw metal additive 102 can beemployed, relative to the aluminum 101. In additional specificembodiments, at least about 3,000 ppmw metal additive 102 can beemployed, relative to the aluminum 101. In additional specificembodiments, at least about 3,500 ppmw metal additive 102 can beemployed, relative to the aluminum 101. In additional specificembodiments, at least about 4,000 ppmw metal additive 102 can beemployed, relative to the aluminum 101. In additional specificembodiments, at least about 4,500 ppmw metal additive 102 can beemployed, relative to the aluminum 101. In additional specificembodiments, at least about 5,000 ppmw metal additive 102 can beemployed, relative to the aluminum 101.

In specific embodiments, up to about 5,000 ppmw metal additive 102 canbe employed, relative to the aluminum 101. In additional specificembodiments, up to about 4,500 ppmw metal additive 102 can be employed,relative to the aluminum 101. In additional specific embodiments, up toabout 4,000 ppmw metal additive 102 can be employed, relative to thealuminum 101. In additional specific embodiments, up to about 3,500 ppmwmetal additive 102 can be employed, relative to the aluminum 101. Inadditional specific embodiments, up to about 3,000 ppmw metal additive102 can be employed, relative to the aluminum 101. In additionalspecific embodiments, up to about 2,500 ppmw metal additive 102 can beemployed, relative to the aluminum 101. In additional specificembodiments, up to about 2,000 ppmw metal additive 102 can be employed,relative to the aluminum 101. In additional specific embodiments, up toabout 1,500 ppmw metal additive 102 can be employed, relative to thealuminum 101. In additional specific embodiments, up to about 1,000 ppmwmetal additive 102 can be employed, relative to the aluminum 101.

In specific embodiments, titanium is employed as a metal additive toform the molten liquid. In further specific embodiments, titanium isemployed as a metal additive to form the molten liquid and the titaniumforms TiB₂. In further specific embodiments, when the titanium formsTiB₂, a relatively long settling time in a quiet bath of molten melt isemployed. Typically a long settling time facilitates the settling (ordropping) of the higher density TiB₂ to the bottom of the vessel. Inspecific embodiments, a settling time of at least 2 hours can beemployed. In additional specific embodiments, a settling time of atleast 3 hours can be employed. In additional specific embodiments, asettling time of at least 4 hours can be employed. In additionalspecific embodiments, a settling time of at least 5 hours can beemployed. In additional specific embodiments, a settling time of atleast 6 hours can be employed.

In specific embodiments, the settling is carried out in a relativelyquiet bath of molten melt. In additional specific embodiments, the meltis not mixed, either by mechanical means or by simple convection. Inadditional specific embodiments, excessive temperatures are avoidedduring the settling. In additional specific embodiments, a temperaturehigh enough to ensure the metal remains completely molten is applied.

In specific embodiments, the aluminum 101 can include at least about0.35 ppmw boron. In additional specific embodiments, the aluminum 101can include at least about 0.40 ppmw boron. In additional specificembodiments, the aluminum 101 can include at least about 0.45 ppmwboron. In additional specific embodiments, the aluminum 101 can includeat least about 0.50 ppmw boron. In additional specific embodiments, thealuminum 101 can include at least about 0.55 ppmw boron. In additionalspecific embodiments, the aluminum 101 can include at least about 0.60ppmw boron. In additional specific embodiments, the aluminum 101 caninclude about 0.30 ppmw to about 0.70 ppmw boron. In additional specificembodiments, the aluminum 101 can include about 0.40 ppmw to about 0.60ppmw boron.

In specific embodiments, the cooling 112 can be carried out at atemperature of at least about 20° C. In additional specific embodiments,the cooling 112 can be carried out at a temperature of about 0° C. toabout 60° C. In additional specific embodiments, the cooling 112 can becarried out at a temperature of about 15° C. to about 40° C. Inadditional specific embodiments, the cooling 112 can be carried out at arate of up to about 500° C./hr, up to about 250° C./hr, up to about 125°C./hr, up to about 100° C./hr, or up to about 75° C./hr.

In specific embodiments, the purified solid aluminum 118 can includeless than about 0.55 ppmw boron. In additional specific embodiments, thepurified solid aluminum 118 can include less than about 0.40 ppmw boron.In additional specific embodiments, the purified solid aluminum 118 caninclude less than about 0.25 ppmw boron. In additional specificembodiments, the purified solid aluminum 118 can include less than about0.20 ppmw boron. In additional specific embodiments, the purified solidaluminum 118 can include less than about 0.15 ppmw boron. In additionalspecific embodiments, the purified solid aluminum 118 can include lessthan about 0.10 ppmw boron.

In specific embodiments, at least about 25 wt. % of boron present in thestarting aluminum 101 can be removed to provide the purified solidaluminum 118. In additional specific embodiments, at least about 35 wt.% of boron present in the starting aluminum 101 can be removed toprovide the purified solid aluminum 118. In additional specificembodiments, at least about 50 wt. % of boron present in the startingaluminum 101 can be removed to provide the purified solid aluminum 118.In additional specific embodiments, at least about 65 wt. % of boronpresent in the starting aluminum 101 can be removed to provide thepurified solid aluminum 118.

In specific embodiments, the heating of the aluminum 301 and titanium302 can be carried out, to achieve a temperature of at least about 750°C. In additional specific embodiments, the heating of the aluminum 301and titanium 302 can be carried out, to achieve a temperature of atleast about 950° C. In additional specific embodiments, the heating ofthe aluminum 301 and titanium 302 can be carried out, to achieve atemperature of about 650° C. to about 1750° C. In additional specificembodiments, the heating of the aluminum 301 and titanium 302 can becarried out, to achieve a temperature of about 700° C. to about 1670° C.

In specific embodiments, at least about 500 ppmw titanium 302 can beemployed, relative to the aluminum 301. In additional specificembodiments, at least about 1,000 ppmw titanium 302 can be employed,relative to the aluminum 301. In additional specific embodiments, atleast about 1,200 ppmw titanium 302 can be employed, relative to thealuminum 301.

In specific embodiments, the aluminum 301 can include at least about0.35 ppmw boron. In additional specific embodiments, the aluminum 301can include at least about 0.40 ppmw boron. In additional specificembodiments, the aluminum 301 can include at least about 0.45 ppmwboron. In additional specific embodiments, the aluminum 301 can includeat least about 0.50 ppmw boron. In additional specific embodiments, thealuminum 301 can include at least about 0.55 ppmw boron. In additionalspecific embodiments, the aluminum 301 can include at least about 0.60ppmw boron. In additional specific embodiments, the aluminum 301 caninclude about 0.30 ppmw to about 0.70 ppmw boron. In additional specificembodiments, the aluminum 301 can include about 0.40 ppmw to about 0.60ppmw boron.

In specific embodiments, the cooling 312 can be carried out at atemperature of at least about 20° C. In additional specific embodiments,the cooling 312 can be carried out at a temperature of about 0° C. toabout 60° C. In additional specific embodiments, the cooling 312 can becarried out at a temperature of about 15° C. to about 40° C. Inadditional specific embodiments, the cooling 312 can be carried out at arate of up to about 500° C./hr, up to about 250° C./hr, up to about 125°C./hr, up to about 100° C./hr, or up to about 75° C./hr.

In specific embodiments, the purified solid aluminum 318 can includeless than about 0.55 ppmw boron. In additional specific embodiments, thepurified solid aluminum 318 can include less than about 0.40 ppmw boron.In additional specific embodiments, the purified solid aluminum 318 caninclude less than about 0.25 ppmw boron. In additional specificembodiments, the purified solid aluminum 318 can include less than about0.20 ppmw boron.

In specific embodiments, at least about 25 ppmw of boron present in thestarting aluminum 301 can be removed to provide the purified solidaluminum 318. In additional specific embodiments, at least about 35 ppmwof boron present in the starting aluminum 301 can be removed to providethe purified solid aluminum 318. In additional specific embodiments, atleast about 50 ppmw of boron present in the starting aluminum 301 can beremoved to provide the purified solid aluminum 318. In additionalspecific embodiments, at least about 65 ppmw of boron present in thestarting aluminum 301 can be removed to provide the purified solidaluminum 318.

In specific embodiments, the silicon 201 can include metallurgical grade(MG) silicon. In additional specific embodiments, the silicon 201 can beof a grade or quality that is below metallurgical grade (MG) silicon. Inadditional specific embodiments, the silicon 201 can be below about 98wt. % pure. In additional specific embodiments, the silicon 201 can bebelow about 95 wt. % pure. In additional specific embodiments, thesilicon 201 can be below about 90 wt. % pure. In additional specificembodiments, the silicon 201 can be below about 85 wt. % pure. Inadditional specific embodiments, the silicon 201 can be below about 80wt. % pure. In additional specific embodiments, the silicon 201 can bebelow about 75 wt. % pure. In additional specific embodiments, thesilicon 201 can be below about 70 wt. % pure. In additional specificembodiments, the silicon 201 can be below about 65 wt. % pure. Inadditional specific embodiments, the silicon 201 can be below about 60wt. % pure.

In specific embodiments, heating 204 of the aluminum 202 and silicon 201can be carried out, to achieve a temperature of at least about 1450° C.In additional specific embodiments, the heating 204 of the aluminum 202and silicon 201 can be carried out, to achieve a temperature of at leastabout 1500° C. In additional specific embodiments, heating 204 of thealuminum 202 and silicon 201 can be carried out, to achieve atemperature of at least about 1550° C. In additional specificembodiments, heating 204 of the aluminum 202 and silicon 201 can becarried out, to achieve a temperature of at least about 1600° C. Inadditional specific embodiments, heating 204 of the aluminum 202 andsilicon 201 can be carried out, to achieve a temperature of at leastabout 1700° C.

In specific embodiments, the aluminum 202 can include up to severalthousand (e.g., 4,000) parts per million (weight) of boron. In suchembodiments, the crude aluminum can be “recycled” aluminum that isobtained, e.g., from the electrical industry. Such aluminum will includethe relatively large amount of boron due to the boron being added toremove substances, such as titanium, from the aluminum. In additionalspecific embodiments, the aluminum 202 can include up to about 3 ppmwboron. In additional specific embodiments, the aluminum 202 can includeup to about 0.60 ppmw boron. In additional specific embodiments, thealuminum 202 can include up to about 0.55 ppmw boron. In additionalspecific embodiments, the aluminum 202 can include up to about 0.50 ppmwboron. In additional specific embodiments, the aluminum 202 can includeup to about 0.45 ppmw boron. In additional specific embodiments, thealuminum 202 can include up to about 0.40 ppmw boron. In additionalspecific embodiments, the aluminum 202 can include up to about 0.25 ppmwboron. In additional specific embodiments, the aluminum 202 can includeup to about 0.20 ppmw boron.

In specific embodiments, the cooling 208 can be carried out at atemperature of at least about 10° C. In additional specific embodiments,the cooling 208 can be carried out at a temperature of at least about15° C. In additional specific embodiments, the cooling 208 can becarried out at a temperature of up to about 50° C. In additionalspecific embodiments, the cooling 208 can be carried out at atemperature of up to about 40° C. In additional specific embodiments,the cooling 208 can be carried out at a temperature of about 10° C. toabout 50° C. In additional specific embodiments, the cooling 208 can becarried out at a temperature of about 15° C. to about 40° C.

In specific embodiments, the cooling 208 can be carried out at a rate ofup to about 125° C./hr. In additional specific embodiments, the cooling208 can be carried out at a rate of up to about 100° C./hr. Inadditional specific embodiments, the cooling 208 can be carried out at arate of up to about 75° C./hr.

In specific embodiments, the molten liquid 206 can be cooled 208 closeto, but above the solidus temperature (e.g., within about 200° C. abovethe solidus temperature, within about 125° C. above the solidustemperature, or within about 50° C. above the solidus temperature). Inadditional specific embodiments, the molten liquid 206 can be cooled 208to a temperature of about 700° C. to about 750° C. In additionalspecific embodiments, the molten liquid 206 can be cooled 208 to abovethe solidus temperature and below the liquidus temperature. Inadditional specific embodiments the molten liquid 206 may be cooled 208to a temperature below the liquidus temperature.

In specific embodiments, the molten liquid 206 can be cooled 208 at arate of up to about 100° C./hr. In additional specific embodiments, themolten liquid 206 can be cooled 208 at a rate of up to about 50° C./hr.In additional specific embodiments, the molten liquid 206 can be cooled208 at a rate of up to about 20° C./hr.

In specific embodiments, the molten liquid 206 can be cooled 208 over aperiod of time of at least about 2 hours. In additional specificembodiments, the molten liquid 206 can be cooled 208 over a period oftime of at least about 4 hours. In additional specific embodiments, themolten liquid 206 can be cooled 208 over a period of time of at leastabout 8 hours. In additional specific embodiments, the molten liquid 206can be cooled 208 over a period of time of at least about 12 hours. Inadditional specific embodiments, the molten liquid 206 can be cooled 208over a period of time of at least about 24 hours. In additional specificembodiments, the molten liquid 206 can be cooled 208 over a period oftime of at least about 48 hours.

In specific embodiments, the silicon crystals 214 can include less thanabout 0.50 ppmw boron. In additional specific embodiments, the siliconcrystals 214 can include less than about 0.45 ppmw boron. In additionalspecific embodiments, the silicon crystals 214 can include less thanabout 0.40 ppmw boron. In additional specific embodiments, the siliconcrystals 214 can include less than about 0.35 ppmw boron. In additionalspecific embodiments, the silicon crystals 214 can include less thanabout 0.30 ppmw boron. In additional specific embodiments, the siliconcrystals 214 can include less than about 0.25 ppmw boron. In additionalspecific embodiments, the silicon crystals 214 can include less thanabout 0.20 ppmw boron.

In specific embodiments, at least about 25 wt. % of boron present in thestarting silicon 201 can be removed to provide the silicon crystals 214.In additional specific embodiments, at least about 30 wt. % of boronpresent in the starting silicon 201 can be removed to provide thesilicon crystals 214. In additional specific embodiments, at least about35 wt. % of boron present in the starting silicon 201 can be removed toprovide the silicon crystals 214. In additional specific embodiments, atleast about 40 wt. % of boron present in the starting silicon 201 can beremoved to provide the silicon crystals 214. In additional specificembodiments, at least about 45 wt. % of boron present in the startingsilicon 201 can be removed to provide the silicon crystals 214. Inadditional specific embodiments, at least about 50 wt. % of boronpresent in the starting silicon 201 can be removed to provide thesilicon crystals 214. In additional specific embodiments, at least about55 wt. % of boron present in the starting silicon 201 can be removed toprovide the silicon crystals 214. In additional specific embodiments, atleast about 60 wt. % of boron present in the starting silicon 201 can beremoved to provide the silicon crystals 214. In additional specificembodiments, at least about 65 wt. % of boron present in the startingsilicon 201 can be removed to provide the silicon crystals 214. Inadditional specific embodiments, at least about 70 wt. % of boronpresent in the starting silicon 201 can be removed to provide thesilicon crystals 214. In additional specific embodiments, at least about75 wt. % of boron present in the starting silicon 201 can be removed toprovide the silicon crystals 214. In additional specific embodiments, atleast about 80 wt. % of boron present in the starting silicon 201 can beremoved to provide the silicon crystals 214.

In specific embodiments, the silicon crystals 214 can include silicon inat least about 70 wt. %. In additional specific embodiments, the siliconcrystals 214 can include silicon in at least about 75 wt. %. Inadditional specific embodiments, the silicon crystals 214 can includesilicon in at least about 80 wt. %. In additional specific embodiments,the silicon crystals 214 can include silicon in at least about 85 wt. %.In additional specific embodiments, the silicon crystals 214 can includesilicon in at least about 90 wt. %. In additional specific embodiments,the silicon crystals 214 can include silicon in at least about 95 wt. %.In additional specific embodiments, the silicon crystals 214 can includesilicon in at least about 96 wt. %. In additional specific embodiments,the silicon crystals 214 can include silicon in at least about 97 wt. %.In additional specific embodiments, the silicon crystals 214 can includesilicon in at least about 98 wt. %. In additional specific embodiments,the silicon crystals 214 can include silicon in at least about 99 wt. %.

Specific enumerated embodiments [1] to [39] provided below are forillustration purposes only, and do not otherwise limit the scope of thedisclosed subject matter, as defined by the claims. These enumeratedembodiments encompass all combinations, sub-combinations, and multiplyreferenced (e.g., multiply dependent) combinations described therein.

Enumerated Embodiments

[1.] A method for purifying aluminum, the method including:

-   -   (a) forming a molten liquid from aluminum and a metal additive        selected from at least one of titanium, vanadium, zirconium, and        chromium;    -   (b) allowing impurities to form in the molten liquid, wherein        the impurities include a reaction product of the metal additive        and boron;    -   (b) optionally removing at least a portion of the impurities        from the molten liquid;    -   (d) cooling the molten liquid to form solidified aluminum; and    -   (e) optionally removing a portion of the solidified aluminum        including at least a portion of the impurities;    -   wherein at least one of the optional steps is carried out, to        provide purified aluminum.

[2.] The method of embodiment [1], wherein at least some boron isremoved, such that the purified aluminum contains less boron than thealuminum in step (a).

[3.] The method of any one of embodiments [1]-[2], wherein the purifiedaluminum includes less than about 0.55 ppmw boron.

[4.] The method of any one of embodiments [1]-[2], wherein the purifiedaluminum includes less than about 0.40 ppmw boron.

[5.] The method of any one of embodiments [1]-[2], wherein the purifiedaluminum includes less than about 0.25 ppmw boron.

[6.] The method of any one of embodiments [1]-[5], wherein the moltenliquid is formed at a temperature of at least about 650° C.

[7.] The method of any one of embodiments [1]-[6], wherein at leastabout 200 ppmw metal additive is employed, relative to the aluminum.

[8.] The method of any one of embodiments [1]-[6], wherein at leastabout 500 ppmw metal additive is employed, relative to the aluminum.

[9.] The method of any one of embodiments [1]-[6], wherein at leastabout 1,000 ppmw metal additive is employed, relative to the aluminum.

[10.] The method of any one of embodiments [1]-[9], wherein metaladditive includes titanium.

[11.] The method of any one of embodiments [1]-[10], wherein thealuminum in step (a) includes at least about 0.40 ppmw boron.

[12.] The method of any one of embodiments [1]-[10], wherein thealuminum in step (a) includes about 0.40 ppmw to about 0.60 ppmw boron.

[13.] The method of any one of embodiments [1]-[12], wherein theimpurities that include a reaction product of metal additive and boroninclude titanium diboride (TiB₂).

[14.] The method of any one of embodiments [1]-[13], wherein theremoving of the portion of the solidified aluminum is carried outmechanically.

[15.] The method of any one of embodiments [1]-[13], wherein theremoving of the portion of the solidified aluminum is carried out bycutting the solidified aluminum.

[16.] The method of any one of embodiments [1]-[15], wherein thealuminum and metal additive are present together in the aluminum in step(a).

[17.] The method of any one of embodiments [1]-[15], wherein the metaladditive is added to the aluminum in step (a), is added to the moltenliquid, or a combination thereof

[18.] The method of any one of embodiments [1]-[17], wherein theimpurities that include the reaction product of metal additive and boroninclude a reaction product of metal additive, boron, and an additionalsubstance present in the molten liquid or which contacts the moltenliquid.

[19.] The method of any one of embodiments [1]-[17], wherein theoptional step of removing the at least a portion of the impurities fromthe molten liquid is carried out.

[20.] The method of any one of embodiments [1]-[17], wherein theoptional step of removing the at least a portion of the impurities fromthe molten liquid is not carried out.

[21.] The method of any one of embodiments [1]-[17], wherein theoptional step of removing a portion of the solidified aluminum includingat least a portion of the impurities is carried out.

[22.] The method of any one of embodiments [1]-[17], wherein theoptional step of removing a portion of the solidified aluminum includingat least a portion of the impurities is not carried out.

[23.] The method of any one of embodiments [1]-[17], wherein theoptional step of removing the at least a portion of the impurities fromthe molten liquid is carried out, and the optional step of removing aportion of the solidified aluminum including at least a portion of theimpurities is carried out.

[24.] The method of any one of embodiments [1]-[23], which is carriedout two or more times.

[25.] A method for purifying silicon, the method including:

-   -   (a) forming a molten liquid from silicon and aluminum, wherein        the aluminum includes less than about 0.55 ppmw boron;    -   (b) cooling the molten liquid, to form silicon crystals and a        mother liquor; and    -   (e) separating the silicon crystals and the mother liquor.

[26.] The method of embodiment [25], wherein the aluminum includes thepurified aluminum or solidified aluminum as recited in any one ofembodiments [1]-[24].

[27.] The method of embodiment [25], wherein the aluminum includes lessthan about 0.25 ppmw boron.

[28.] The method of embodiment [25], wherein the aluminum includes lessthan about 0.10 ppmw boron.

[29.] The method of any one of embodiments [25]-[28], wherein thesilicon crystals include less than about 0.40 ppmw boron.

[30.] The method of any one of embodiments [25]-[27], wherein thesilicon crystals include less than about 0.25 ppmw boron.

[31.] The method of any one of embodiments [25]-[28], wherein thesilicon crystals include about 0.20 ppmw boron.

[32.] The method of any one of embodiments [25]-[31], wherein in step(a), the silicon is metallurgical grade (MG) silicon.

[33.] The method of any one of embodiments [25]-[31], wherein in step(a), the silicon is employed in about 20 wt. % to about 50 wt. %.

[34.] The method of any one of embodiments [25]-[32], wherein in step(a), the aluminum is employed in about 50 wt. % to about 80 wt. %.

[35.] The method of any one of embodiments [25]-[34], wherein in step(b), the molten liquid is cooled at a rate of less than about 75° C./hr.

[36.] The method of any one of embodiments [25]-[35], wherein in step(b), the molten liquid is cooled over a period of time of at least about2 hours.

[37.] The method of any one of embodiments [25]-[36], wherein step (c)is carried out by pouring off the mother liquor from the siliconcrystals.

[38.] The method of any one of embodiments [25]-[37], wherein thesilicon crystals include silicon in at least about 65 wt. %.

[39.] The method of any one of embodiments [25]-[38], which is carriedout two or more times.

EXAMPLES Example 1

The graph below illustrates the level of boron present in siliconflakes, for samples of silicon flakes obtained over a period of time.

1. A method for purifying aluminum, the method comprising: (a) forming amolten liquid from aluminum and a metal additive selected from at leastone of titanium, vanadium, zirconium, and chromium; (b) allowingimpurities to form in the molten liquid, wherein the impurities comprisea reaction product of the metal additive and boron; (b) optionallyremoving at least a portion of the impurities from the molten liquid;(d) cooling the molten liquid to form solidified aluminum; and (e)optionally removing a portion of the solidified aluminum comprising atleast a portion of the impurities; wherein at least one of the optionalsteps is carried out, to provide purified aluminum.
 2. The method ofclaim 1, wherein at least some boron is removed, such that the purifiedaluminum contains less boron than the aluminum in step (a).
 3. Themethod of claim 1, wherein the purified aluminum comprises less thanabout 0.55 ppmw boron. 4-6. (canceled)
 7. The method of claim 1, whereinat least about 200 ppmw metal additive is employed, relative to thealuminum. 8-9. (canceled)
 10. The method of claim 1, wherein metaladditive comprises titanium.
 11. The method of claim 1, wherein thealuminum in step (a) comprises at least about 0.40 ppmw boron. 12.(canceled)
 13. The method of claim 1, wherein the impurities thatcomprise a reaction product of metal additive and boron comprisetitanium diboride (TiB₂). 14-16. (canceled)
 17. The method of claim 1,wherein the metal additive is added to the aluminum in step (a), isadded to the molten liquid, or a combination thereof 18-19. (canceled)20. The method of claim 1, wherein the optional step of removing the atleast a portion of the impurities from the molten liquid is not carriedout.
 21. (canceled)
 22. The method of claim 1, wherein the optional stepof removing a portion of the solidified aluminum comprising at least aportion of the impurities is not carried out.
 23. The method of claim 1,wherein the optional step of removing the at least a portion of theimpurities from the molten liquid is carried out, and the optional stepof removing a portion of the solidified aluminum comprising at least aportion of the impurities is carried out.
 24. The method of claim 1,which is carried out two or more times.
 25. A method for purifyingsilicon, the method comprising: (a) forming a molten liquid from siliconand aluminum, wherein the aluminum comprises less than about 0.55 ppmwboron; (b) cooling the molten liquid, to form silicon crystals and amother liquor; and (c) separating the silicon crystals and the motherliquor. 26-27. (canceled)
 28. The method of claim 25, wherein thealuminum comprises less than about 0.10 ppmw boron.
 29. The method ofclaim 25, wherein the silicon crystals comprise less than about 0.40ppmw boron.
 30. (canceled)
 31. The method of claim 25, wherein thesilicon crystals comprise about 0.20 ppmw boron.
 32. The method of claim25, wherein in step (a), the silicon is metallurgical grade (MG)silicon.
 33. The method of claim 25, wherein in step (a), the silicon isemployed in about 20 wt. % to about 50 wt. %. 34-37. (canceled)
 38. Themethod of claim 25, wherein the silicon crystals comprise silicon in atleast about 65 wt. %.
 39. The method of claim 25, which is carried outtwo or more times.